Glucocorticoids potently regulate ion transport in intestinal epithelia. We present the following hypotheses: 1) Glucocorticoid regulation of epithelial transport is mediated by distinct isoreceptor, receptor IB, suggesting receptor type as well as available nuclear acceptor sites determine physiologic effect. 2) Glucocorticoids maintain electroneutral basal sodium (Na) absorption in intestine through the Na-H antiport. 3) The electroneutral pathway and the electrogenic pathway controlled by the aldosterone receptor are interrelated. Stimulation of one pathway results in inhibition of the other pathway. Our objectives are to 1) purify and characterize receptor IB and to define receptor mediated nuclear events to verify it is a physiologically relevant receptor form. 2) define ion transport pathways controlled by glucocorticoids 3) define the mechanism by which glucocorticoids regulate these pathway and 4) determine the mechanism by which the epithelial cell regulates whether glucocorticoid or aldosterone mediated pathways predominate. Unactivated and activated receptor IB will be purified for determination of its physical characteristics and amino acid sequence of its peptide fragments. These characteristics will be compared to those of the classic receptor II. The nuclear form of IB will be characterized and translocation and DNA chromatin binding affinity and binding sites will be defined. NA-H specific amiloride analog binding studies will be used to determine if glucocorticoids increase the number or affinity of cell membrane antiporters. Measurement of Na+ and H+ flux in colon apical membrane vesicles will determine if glucocorticoids increase the KM or the Vmax of the antiporter for Na+ or H+. Determination of glucocorticoid effect on intracellular pH will indicate whether increased antiport activity is driven by changes in the internal modifier or is secondary to intracellular acidosis. Dependence of transport on transcription and new protein synthesis will be investigated. Glucocorticoid inhibition of aldosterone induced transport will be examined with in vitro transport studies and by determining the effect of glucocorticoids on the number of affinity of conductive sodium channels. If glucocorticoids control intestinal absorption through regulation of Na-H antiport this should be important for understanding and therapy of disorders of intestinal transport. The antiport also plays an important role in several other functions including acid base homeostasis, platelet function, normal cell proliferation and differentiation. Defining the role of glucocorticoids in these processes has important therapeutic implications.